One method to control a variable event valvetrain during an engine start is described in U.S. Pat. No. 5,765,514. This method provides for closing the intake and exhausts valves after the ignition switch is turned on and then allows the starter to crank the engine. If a signal pulse representing crankshaft rotation through 720 degrees has been generated, an injection sequence for each cylinder and a crankshaft position sequence are set. The injection sequence for the cylinders is initialized when a first crankshaft pulse is generated after generation of a first signal pulse representing crankshaft rotation through 720 degrees. The injection sequence and crankshaft position sequence correspond to the position of each cylinder, whereby the opening/closing timing of each intake valve and exhaust valve can be controlled. The cylinders are set to the exhaust stroke, suction stroke, compression stroke, and explosion stroke, respectively.
The above-mentioned method can also have several disadvantages. In particular, the method can reduce valve power consumption but it may also increase engine emissions. For example, the valves can assume the neutral position, where they are open or partially open, without power being supplied to the valves. However, the open valves may permit oxygen to enter the engine and exhaust system. This can permit air to flow through the exhaust system so that the amount of oxygen stored in the catalyst increases, thereby permitting excess oxygen to occupy catalyst sites that might otherwise be available for conversion of undesirable gases. Consequently, valve power consumption may be reduced at the expense of engine emissions. Further, the method appears to execute a single starting sequence and therefore needlessly restricts the functionality of the variable event valvetrain during a start.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method to control engine valves during stopping and starting that offers substantial improvements.